Liquid level indicating

ABSTRACT

In some examples, a liquid container comprises a chamber forming a volume containing a liquid, an elongated strip extending into the volume containing the liquid, the strip supported along a side of the volume such that a face of the strip adjacent the side of the volume is not opposed by the liquid, a plurality of heaters supported by the strip along the strip, and a plurality of temperature sensors supported by the strip along the strip.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 15/839,587, filedDec. 12, 2017, which is a continuation of International Application No.PCT/US2015/057785, filed Oct. 28, 2015, which are both herebyincorporated by reference in their entirety.

BACKGROUND

Various devices are presently employed to sense the level of a liquidwithin a volume. Some of these devices may be relatively complex andexpensive to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a portion of an example liquid interface for anexample liquid level sensor.

FIG. 1B is a diagram of portions of another example liquid interface foran example liquid level sensor.

FIG. 2 is a flow diagram of an example method for determining a level ofliquid using the liquid level sensor of the FIG. 1.

FIG. 3 is a diagram of an example liquid level sensing system.

FIG. 4 is a diagram of an example liquid supply system including theliquid level sensing system of FIG. 3.

FIG. 5 diagram of another example liquid supply system including theliquid level sensing system of FIG. 3.

FIG. 6 is a diagram of a portion of another example liquid interface ofa liquid level sensor.

FIG. 7 is an example circuit diagram of the liquid level sensor of FIG.6.

FIG. 8 is a sectional view of the example liquid interface of FIG. 6.

FIG. 9A is a fragmentary front view of the liquid level sensor of FIG.6, illustrating an example heat spike resulting from the pulsing of aheater.

FIG. 9B is a fragmentary front view of another example liquid levelsensor, illustrating an example heat spike resulting from the pulsing ofa heater.

FIG. 9C is a sectional view of the example liquid level sensor of FIG.9B, illustrating the example heat spike resulting from the pulsing ofthe heater.

FIG. 10 is a graph illustrating an example of different sensedtemperature responses over time to a heater impulse.

FIG. 11 is a diagram of another example liquid level sensor.

FIG. 12 is an enlarged view of a portion of the example liquid levelsensor of FIG. 11.

FIG. 13 is a perspective view of another example liquid level sensor.

FIG. 14 is a front view of the example liquid level sensor of FIG. 13.

FIG. 15 is a sectional view of the example liquid level sensor of FIG.14.

FIG. 16 is a flow diagram of an example method for forming the exampleliquid level sensor of FIG. 13.

FIG. 17 is a front view of an example panel upon which multiple liquidlevel sensors have been formed, prior to singulation.

FIGS. 18A-18E are sectional views illustrating the example liquid levelsensor of FIG. 13 as it is being formed.

DETAILED DESCRIPTION OF EXAMPLES

Many existing devices that are currently used to sense the level of aliquid within a volume may be relatively complex and expensive tomanufacture. For example, many presently available liquid level sensingdevices utilize expensive componentry and expensive materials. Manypresently available liquid level sensing devices involve dedicatedcomplex manufacturing processes.

This disclosure describes various example liquid level sensing liquidinterfaces that are less expensive to manufacture. As will be describedhereafter, in some implementations, the disclosed liquid level sensingliquid interfaces facilitate the use of materials having a wide range oftemperature coefficient of resistance. In some implementations, thedisclosed liquid level sensing liquid interfaces are well adapted forsensing the level of otherwise corrosive liquids without using generallymore expensive corrosive resistant materials.

FIG. 1A illustrates an example liquid level sensing interface 24 for aliquid level sensor. Liquid interface 24 interacts with liquid within avolume 40 and outputs signals that indicate the current level of liquidwithin the volume 40. Such signals are processed to determine the levelof liquid within the volume 40. Liquid interface 24 facilitates thedetection of the level of liquid within the volume 40 in a low-costmanner.

As schematically shown by FIG. 1A, liquid interface 24 comprises strip26, a series 28 of heaters 30 and a series 32 of sensors 34. Strip 26comprises an elongated strip that is to be extended into volume 40containing the liquid 42. Strip 26 supports heaters 30 and sensors 34such that a subset of the heaters 30 and sensors 34 are submersed withinliquid 42, when liquid 42 is present.

In one implementation, strip 26 is supported (from the top or from thebottom) such that those portions of strip 26, and their supportedheaters 30 and sensors 34, submersed within liquid 42, are completelysurrounded on all sides by the liquid 42. In another implementation,strip 16 is supported along a side of the volume 40 such that a face ofstrip 26 adjacent the side of volume 40 is not opposed by the liquid 42.In one implementation, strip 26 comprises an elongated rectangular,substantially flat strip. In another implementation strip 26 comprisesstrip having a different polygon a cross-section or a circular or ovalcross-section.

Heaters 30 comprise individual heating elements spaced along a length ofstrip 26. Each of heaters 30 is sufficiently close to a sensor 28 suchthat the heat emitted by the individual heater may be sensed by theassociated sensor 28. In one implementation, each heater 30 isindependently actuatable to emit heat independent of other heaters 30.In one implementation, each heater 30 comprises an electrical resistor.In one implementation, each heater 30 is to emit a heat pulse forduration of at least 10 μs with a power of at least 10 mW.

In the example illustrated, heaters 30 are employed to emit heat and donot serve as temperature sensors. As a result, each of heaters 30 may beconstructed from a wide variety of electrically resistive materialshaving a wide range of temperature coefficient of resistance. A resistormay be characterized by its temperature coefficient of resistance, orTCR. The TCR is the resistor's change in resistance as a function of theambient temperature. TCR may be expressed in ppm/° C., which stands forparts per million per centigrade degree. The temperature coefficient ofresistance is calculated as follows:

temperature coefficient of a resistor: TCR=(R2−R1)e−6/R1*(T2−T1),

where TCR is in ppm/° C., R1 is in ohms at room temperature, R2 isresistance at operating temperature in ohms, T1 is the room temperaturein ° C. and T2 is the operating temperature in ° C.

Because heaters 30 are separate and distinct from temperature sensors34, a wide variety of thin-film material choices are available in waferfabrication processes for forming heaters 30. In one implementation,each of heaters 30 has a relatively high heat dissipation per area, hightemperature stability (TCR<1000 ppm/° C.), and the intimate coupling ofheat generation to the surrounding medium and heat sensor. Suitablematerials can be refractory metals and their respective alloys such astantalum, and its alloys, and tungsten, and its alloys, to name a few;however, other heat dissipation devices like doped silicon orpolysilicon may also be used.

Sensors 34 comprise individual sensing elements spaced along the lengthof strip 26. Each of sensors 34 is sufficiently close to a correspondingheater 30 such that the sensor 34 may detect or respond to the transferof heat from the associated or corresponding heater 30. Each of sensors34 outputs a signal which indicates or reflects the amount of heattransmitted to the particular sensor 34 following and corresponding to apulse of heat from the associated heater. The amount of the transmittedto the associated heater will vary depending upon the medium throughwhich the heat was transmitted prior to reaching the sensor. Liquid willthermally conduct heat at a faster rate as compared to air. As a result,the differences between signals from sensors 34 indicate the level ofliquid 42 within volume 40.

In one implementation, each of sensors 34 comprises a diode which has acharacteristic temperature response. For example, in one implementation,each of sensors 34 comprises a P-N junction diode. In otherimplementations, other diodes may be employed or other temperaturesensors may be employed.

In the example illustrated, heaters 30 and sensors 34 are supported bystrip 26 so as to be interdigitated or interleaved amongst one anotheralong the length of strip 26. For purposes of this disclosure, the term“support” or “supported by with respect to heaters and/or sensors and astrip means that the heaters and/or sensors are carried by the stripsuch that the strip, heaters and sensors form a single connected unit.Such heaters and sensors may be supported on the outside or within andinterior of the strip. For purposes of this disclosure, the term“interdigitated” or “interleaved” means that two items alternate withrespect to one another. For example, interdigitated heaters and sensorsmay comprise a first heater, followed by a first sensor, followed by asecond heater, followed by a second sensor and so on.

In one implementation, an individual heater 30 may emit pulses of heatthat are to be sensed by multiple sensors 34 proximate to the individualheater 30. In one implementation, each sensor 34 is spaced no greaterthan 20 μm from an individual heater 30. In one implementation, sensors30 have a minimum one-dimensional density along strip 24 of at least 100sensors 34 per inch (at least 40 sensors 34 per centimeter). The onedimensional density comprises a number of sensors per unit measure in adirection along the length of strip 26, the dimension of strip 26extending to different depths, defining the depth or liquid levelsensing resolution of liquid interface 24. In other implementations,sensors 30 have other one dimensional densities along strip 24. Forexample, in another implementation, sensors 34 have a one-dimensionaldensity along strip 26 of at least 10 sensors per inch. In otherimplementations, sensors 34 may have a one-dimensional density alongstrip 26 on the order of 1000 sensors per inch (400 sensors percentimeter) or greater.

In some implementations, the vertical density or number of sensors pervertical centimeter or inch may vary along the vertical or longitudinallength of strip 26. FIG. 1B illustrates an example sensor strip 126having a varying density of sensors 34 along its major dimension orlaunching a length. In the example illustrated, sensor strip 126 hasgreater density of sensors 34 in those regions along the vertical heightor depth may benefit more from a greater degree of depth resolution. Inthe example illustrated, sensor strip 126 has a lower portion 127 havinga first density of sensors 34 and an upper portion 129 having a seconddensity of sensors 34, the second density being less than the firstdensity. In such an implementation, sensor strip 126 provides a higherdegree of accuracy or resolution as the level of the liquid within thevolume approaches an empty state. In one implementation, lower portion127 has a density of at least 40 sensors 34 per centimeter while upperportion 129 has a density of less than 10 sensors per centimeter, and inone implementation, 4 sensors 34 per centimeter. In yet otherimplementations, an upper portion or a middle portion of sensor strip126 may alternatively have a greater density of sensors as compared toother portions of censor strip 126.

Each of heaters 30 and each of sensors 34 are selectively actuatableunder the control of a controller. In one implementation, the controlleris part of or carried by strip 26. In another implementation, thecontroller comprises a remote controller electrically connected to theheaters 30 on strip 26. In one implementation, interface 24 comprises aseparate component from the controller, facilitating replacement ofinterface 24 or facilitating the control of multiple interfaces 24 by aseparate controller.

FIG. 2 is a flow diagram of an example method 100 that may be carriedout using a liquid interface, such as liquid interface 24, to sense anddetermine the level of a liquid within a volume. As indicated by block102, control signals are sent to heaters 30 causing a subset of heaters30 or each of heaters 30 to turn on and off so as to emit a heat pulse.In one implementation, control signals are sent to heaters 30 such thatheaters 30 are sequentially actuated or turned on and off (pulsed) tosequentially emit pulses of heat. In one implementation, the heaters aresequentially turned on and off in order for example, in order from topto bottom along strip 26 or from bottom to top along strip 26.

In another implementation, heaters 30 are actuated based upon a searchalgorithm, wherein the controller identifies which of heaters 30 shouldbe initially pulsed in an effort to reduce the total time or the totalnumber of heaters that are pulsed to determine the level of liquid 42within volume 40. In one implementation, the identification of whatheaters 30 are initially pulsed is based upon historical data. Forexample, in one implementation, the controller consults a memory toobtain data regarding the last sensed level of liquid 42 within volume40 and pulses those heaters 30 most proximate to the last sensed levelof liquid 42 before pulsing other heaters 30 more distant from the lastsensed level of liquid 42.

In another implementation, the controller predicts the current level ofliquid 42 within volume 40 based upon the obtained last sensed level ofliquid 42 and pulses those heaters 30 proximate to the predicted currentlevel of liquid 42 within volume 44 pulsing other heaters 30 moredistant from the predicted current level of liquid 42. In oneimplementation, the predicted current level of liquid 42 is based uponthe last sensed level of liquid 42 and a lapse of time since the lastsensing of the level of liquid 42. In another implementation, thepredicted current level of liquid 42 is based upon the last sensed levelof liquid 42 and data indicating the consumption or withdrawal of liquid42 from the volume. For example, in circumstances where liquid interface42 is sensing the volume of an ink in an ink supply, the predictedcurrent level of liquid 42 may be based upon last sensed level of liquid42 and data such as the number of pages printed using the ink or thelike.

In yet another implementation, heaters 30 may be sequentially pulsed,wherein heaters proximate to a center of the depth range of volume 40are initially pulsed and wherein the other heaters are pulsed in theorder based upon their distance from the center of the depth range ofvolume 40. In yet another implementation, subsets of heaters 30 areconcurrently pulsed. For example, a first heater and a second heater maybe concurrently pulsed where the first heater and the second heater aresufficiently spaced from one another along strip 26 such that the heatemitted by the first heater is not transmitted or does not reach thesensor intended to sense transmission of heat from the second heater.Concurrently pulsing heaters 30 may reduce the total time fordetermining the level of liquid 42 within volume 40.

In one implementation, each heat pulse has a duration at least 10 μs andas a power of at least 10 mW. In one implementation, each heat pulse hasa duration of between 1 and 100 μs and up to a millisecond. In oneimplementation, each heat pulse has a power of at least 10 mW and up toand including 10 W.

As indicated by block 104 in FIG. 2, for each emitted pulse, anassociated sensor 34 senses the transfer of heat from the associatedheater to the associated sensor 34. In one implementation, each sensor34 is actuated, turned on or polled following a predetermined period oftime after the pulse of heat from the associated heater. The period oftime may be based upon the beginning of the pulse, the end of the pulseor some other time value related to the timing of the pulse. In oneimplementation, each sensor 34 senses heat transmitted from theassociated heater 30 beginning at least 10 μs following the end of theheat pulse from the associated heater 30. In one implementation, eachsensor 34 senses heat transmitted from the associated heater 30beginning 1000 μs following the end of the heat pulse from theassociated heater 30. In another implementation, sensor 34 senses 34initiates the sensing of heat after the end of the heat pulse from theassociated heater following a period of time equal to a duration of theheat pulse, wherein such sensing occurs for a period of time of betweentwo to three times the duration of the heat pulse. In yet otherimplementations, the time delay between the heat pulse and the sensingof heat by the associated sensor 34 may have other values.

As indicated by block 106 in FIG. 2, the controller or anothercontroller determines a level of the liquid 42 within the volume 40based upon the sensed transfer of heat from each emitted pulse. Forexample, liquid may transfer or transmit heat at a higher rate ascompared to air. If the level of liquid 42 within volume 40 is such thatliquid is extending between a particular heater 30 and its associatedsensor 34, heat transfer from the particular heater 32 is associatedsensor 34 will be faster as compared to circumstances where air isextending between the particular heater 30 and its associated sensor 34.Based upon the amount of heat sensed by the associated sensor 34following the emission of the heat pulse by the associated heater 30,the controller determines whether air or liquid is extending between theparticular heater 30 and the associated sensor. Using this determinationand the known location of the heater 30 and/or sensor 34 along strip 26and the relative positioning of strip 26 with respect to the floor ofvolume 40, the controller determines the level of liquid 42 withinvolume 40. Based upon the determined level of liquid 42 within volume 40and the characteristics of volume 40, the controller is further able todetermine the actual volume or amount of liquid remaining within volume40.

In one implementation, the controller determines the level of liquidwithin the volume 40 by consulting a lookup table stored in a memory,wherein the lookup table associates different signals from sensors 34with different levels of liquid within volume 40. In yet anotherimplementation, controller determines level liquid within volume 40 byutilizing signals from 34 as input to an algorithm or formula.

In some implementations, method 100 and liquid interface 32 may be usedto not only determine an uppermost level or top surface of liquid withinvolume 40, but also determine different levels of different liquidsconcurrently residing in volume 40. For example, due to differentdensities or other properties, different liquids may layer upon oneanother while concurrently residing in a single volume 40. Each of suchdifferent liquids may have a different heat transfer characteristic. Insuch an application, method 100 and liquid interface 24 may be used toidentify where the layer of a first liquid ends within volume 40 andwhere the layer of a second different liquid, underlying or overlyingthe first liquid, begins.

In one implementation, the determined level (or levels) of liquid withinthe volume 40 and/or the determined volume or amount of liquid withinvolume 40 is output through a display or audible device. In yet otherimplementations, the determined level of liquid or the volume of liquidis used as a basis for triggering an alert, warning or the like to user.In some implementations, the determined level of liquid or volume ofliquid is used to trigger the automatic reordering of replenishmentliquid or the closing of a valve to stop the inflow of liquid into thevolume 40. For example, in printers, the determined level of liquidwithin volume 40 may automatically trigger reordering of the replacementink cartridge or replacement ink supply.

FIG. 3 illustrates an example liquid level sensing system 220. Liquidlevel sensing system 220 comprises carrier 222, liquid interface 24(described above), electrical interconnect 226, controller 230 anddisplay 232. Carrier 222 comprises a structure that supports strip 26.In one implementation, carrier 222 comprises a strip formed from, orcomprise, a polymer, glass or other material. In one implementation,carrier 222 has embedded electrical traces or conductors. For example,in one implementation, carrier 222 comprises composite material composedof woven fiberglass cloth with an epoxy resin binder. In oneimplementation, carrier 222 comprises a glass-reinforced epoxy laminatesheet, tube, rod or printed circuit board.

Liquid interface 24, described above, extends along a length of carrier222. In one implementation, liquid interface 24 is glued, bonded orotherwise affixed to carrier 222. In some implementations, dependingupon the thickness and strength of strip 26, carrier 222 may be omitted.

Electrical interconnect 226 comprises an interface by which signals fromthe sensors 34 (shown in FIG. 1) of interface 24 are transmitted tocontroller 230. In one implementation, electrical interconnect 226comprises electrical contact pads 236. In other implementations,electrical interconnect 226 may have other forms. Electricalinterconnect 226, carrier 222 and strip 24, collectively, form a liquidlevel sensor 200 that may be incorporated into and fixed as part of aliquid container volume or may be a separate portable sensing devicewhich may be temporarily manually inserted into different liquidcontainers or volumes.

Controller 230 comprises a processing unit 240 and associatednon-transient computer-readable medium or memory 242. In oneimplementation, controller 230 is separate from liquid level sensor 200.In other implementations, controller 230 is incorporated as part ofsensor 200. Processing unit 240 files instructions contained in memory242. For purposes of this application, the term “processing unit” shallmean a presently developed or future developed processing unit thatexecutes sequences of instructions contained in a memory. Execution ofthe sequences of instructions causes the processing unit to performsteps such as generating control signals. The instructions may be loadedin a random access memory (RAM) for execution by the processing unitfrom a read only memory (ROM), a mass storage device, or some otherpersistent storage. In other embodiments, hard wired circuitry may beused in place of or in combination with software instructions toimplement the functions described. For example, controller 230 may beembodied as part of one or more application-specific integrated circuits(ASICs). Unless otherwise specifically noted, the controller is notlimited to any specific combination of hardware circuitry and software,nor to any particular source for the instructions executed by theprocessing unit.

Processing unit 240, following instructions contained in memory 242carries out method 100 shown and described above with respect to FIG. 2.Processor 240, following instructions provided in memory 242,selectively pulses heaters 30. Processor 240, following instructionsprovided in memory 242, obtains data signals from sensors 34, or in thedata signals indicate dissipation of heat from the pulses and thetransfer of heat to the sensors 34. Processor 240, followinginstructions provided in memory 242, determines a level of liquid withinthe volume based upon the signals from sensors 34. As noted above, insome implementations, controller 230 may additionally determine anamount or volume of liquid using characteristics of the volume orchamber containing a liquid. In one implementation,

Display 232 receives signals from controller 230 and presents visibledata based upon the determined level of liquid and/or determined volumeor amount of liquid within the volume. In one implementation, display232 presents an icon or other graphic depicting a percentage of thevolume that is filled with the liquid. In another implementation,display 232 presents an alphanumeric indication of the level of liquidor percent of the volume that is filled with the liquid or that has beenemptied of the liquid. In yet another implementation, display 232presents an alert or “acceptable” status based on the determined levelliquid within the volume. In yet other implementations, display 232 maybe omitted, wherein the determined level of liquid within the volume isused to automatically trigger an event such as the reordering ofreplenishment liquid, the actuation of a valve to add a liquid to thevolume or the actuation of valve to terminate the ongoing addition ofliquid to the volume.

FIG. 4 is a sectional view illustrating liquid level sensing system 220incorporated as part of a liquid supply system 310. Liquid supply system310 comprises liquid container 312, chamber 314 and fluid or liquidports 316. The container 312 defines chamber 314. Chamber 314 forms anexample volume 40 in which liquid 42 is contained. As shown by FIG. 4,carrier 222 and liquid interface 24 project into chamber 314 from abottom side of chamber 314, facilitating liquid level determinations aschamber 314 nears a state of being completely empty. In otherimplementations, carrier 222 in liquid interface 24 may alternatively besuspended from a top of chamber 314.

Liquid ports 316 comprise liquid passes by which liquid from withinchamber 314 is delivered are directed to an external recipient. In oneimplementation, liquid ports 316 comprise a valve or other mechanismfacilitating selective discharge of liquid from chamber 314. In oneimplementation, liquid supply system 310 comprises an off-axis inksupply for a printing system. In another implementation, liquid supplysystem 310 additionally comprises a print head 320 which is fluidlycoupled to chamber 314 to receive liquid from chamber 314 through liquidinterface 316. For example, in one implementation, liquid supply system310, including print head 320, may form a print cartridge. For purposesof this disclosure, the term “fluidly coupled” means that two or morefluid transmitting volumes are connected directly to one another or areconnected to one another by intermediate volumes or spaces such thatfluid may flow from one volume into the other volume.

In the example illustrated in FIG. 4, communication between controller230, which is remote or separate from liquid supply system tuner and 10,is facilitated via a wiping connector 324 such as a universal serial busconnector or other type of connector. Controller 230 and display 232operate as described above.

FIG. 5 is a sectional view illustrating liquid supply system 410,another example implementation of liquid supply system 310. Liquidsupply system 410 is similar to liquid supply system 310 except thatliquid supply system 410 comprises liquid port 416 in place of liquidport 316. Liquid port 416 is similar to liquid interface 316 except thatliquid port 416 is provided in a cap 426 above chamber 314 of container312. Those remaining components of system 410 which correspond tocomponents of system 310 are numbered similarly.

FIGS. 6-8 illustrate liquid level sensor 500, one example of the liquidlevel sensor 200. FIG. 6 is a diagram illustrating a portion of liquidinterface 224. FIG. 7 is a circuit diagram of sensor 500. FIG. 8 is asectional view through liquid interface 224 of FIG. 6 taken along lines8-8. As shown by FIG. 6, liquid interface 224 is similar to liquidinterface 24 described above in that liquid interface 224 comprisesstrip 26 which supports a series of heaters 530 and a series oftemperature sensors 534. In the example illustrated, heaters 530 andtemperature sensors 534 are interdigitated or interleaved along thelength L of strip 26, wherein the length L is the major dimension ofstrip 26 to extend across different depths when sensor 500 is beingused. In the example illustrated, each sensor 534 is spaced from itsassociated or corresponding heater 530 by a spacing distance S, asmeasured in a direction along the length L, of less than or equal to 20μm and nominally 10 μm. In the example illustrated, the sensors 534 andtheir associated heaters 530 are arranged in pairs, wherein the heaters530 of adjacent pairs are separated from one another by a distance D, asmeasured in a direction along the length L of at least 25 μm to reducethermal cross talk between consecutive heaters. In one implementation,consecutive heaters 530 are separated from one another by a distance Dof between 25 μm and 2500 μm, and nominally 100 μm.

As shown by FIG. 7, in the example illustrated, each heater 530comprises an electrical resistor 550 which may be selectively turn onand off through the selective actuation of a transistor 552. Each sensor534 comprises a diode 560. In one implementation, diode 560, serving astemperature sensors, comprise a P-N junction diode. Each diode 550 has acharacteristic response to changes in temperature. In particular, eachdiode 550 has a forward voltage that changes in response to changes intemperature. Diode 550 exhibit a nearly linear relationship betweentemperature and applied voltage. Because temperature sensors 530comprise diodes or semiconductor junctions, sensor 500 has a lower costand they can be fabricated upon stripper 26 using semiconductorfabrication techniques.

FIG. 8 is a sectional view of a portion of one example of sensor 500. Inthe example illustrated, strip 26 is supported by carrier 222 (describedabove). In one implementation, strip 26 comprises silicon while carrier122 comprises a polymer or plastic. In the example illustrated, heater530 comprises a polysilicon heater which is supported by strip 26, butseparated from strip 26 by an electrically insulating layer 562, such asa layer of silicon dioxide iln the example illustrated, heater 530 isfurther encapsulated by an outer passivation layer 564 which inhibitscontact of between heater 530 and the liquid being sensed. Layer 564protects heater 530 and sensors 534 from damage that would otherwiseresult from corrosive contact with the liquid or ink being sensed. Inone implementation, the outer passivation layer 564 comprises siliconcarbide and/or tetraethyl orthosilicate (TEOS). In otherimplementations, layers 562, 564 may be omitted or may be formed fromother materials.

As shown by FIGS. 7 and 8, the construction of sensor 500 createsvarious layers or barriers providing additional thermal resistances R.The pulse of heat emitted by heater 530 is transmitted across suchthermal resistances to the associated sensor 534. The rate at which theheat from a particular heater 530 is transmitted to the associatedsensor 534 varies depending upon whether the particular heater 530 isbordered by air 41 or liquid 42. Signals from sensor 534 will varydepending upon whether they were transmitted across air 41 are liquid42. Differences signals are used to determine the current level ofliquid within a volume.

FIGS. 9A, 9B and 9C illustrate liquid interfaces 624 and 644, otherexample implementations of liquid interface 24. In FIG. 9A, heaters andsensors are arranged in pairs labeled 0, 1, 2, . . . N. Liquid interface624 is similar to liquid interface 24 except that rather than beinginterleaved or interdigitated vertically along the length of strip 26,heaters 30 and sensors 34 are arranged in an array of side-by-side pairsvertically along the length of strip 26.

FIGS. 9B and 9C illustrate liquid interface 644, another exampleimplementation of liquid interface 24. Liquid interface 644 similar toliquid interface 24 except that the heaters 30 and sensors 34 arearranged in an array of stacks vertically spaced along the length ofstrip 26. FIG. 9C is a sectional view of interface 644 furtherillustrating the stacked arrangement of the pairs of heaters 30 andsensors 34.

FIGS. 9A-9C additionally illustrate an example pulsing of the heater 30of heater/sensor pair 1 and the subsequent dissipation of heat throughthe adjacent materials. In FIGS. 9A-9C, the temperature or intensity ofthe heat dissipates or declines as the heat travels further away fromthe source of the heat, heater 30 of heater/sensor pair 1. Thedissipation of heat is illustrated by the change crosshatching in theFigures.

FIG. 10 illustrate a pair of time synchronized graphs of the examplepulsing shown in FIGS. 9A-9C. FIG. 10 illustrates the relationshipbetween the pulsing of the heater 30 of heater sensor pair 1 and theresponse over time by sensors 34 of heater/sensor pairs 0, 1 and 2. Asshown by 10, the response of each of sensors 34 of each pairs 0, 1 and 2varies depending upon whether air or liquid is over or adjacent to therespective heater/sensor pair 0, 1 and 2. The characteristic transientcurve and magnitude scale differently in the presence of air versus thepresence of liquid. As a result, signals from interface 644, as well asother interfaces such as interfaces 24 and 624, indicate the level ofliquid within the volume.

In one implementation, a controller, such as controller 230 describedabove, determines a level of liquid within the sensed volume byindividually pulsing the heater 30 of a pair and comparing the magnitudeof the temperature, as sensed from the sensor of the same pair, relativeto the heater pulsing parameters to determine whether liquid or air isadjacent to the individual heater/sensor pair. Controller 230 carriesout such pulsing and sensing for each pair of the array until the levelof the liquid within the sensed volume is found or identified. Forexample, controller 230 may first pulse heater 30 of pair 0 and comparethe sensed temperature provided by sensor 34 of pair 0 to apredetermined threshold. Thereafter, controller 30 may pulse heater 30of pair 1 and compare the sensed temperature provided by sensor 34 ofpair 1 to a predetermined threshold. This process is repeated until thelevel of the liquid is found or identified.

In another implementation, a controller, such as controller 230described above, determines a level of liquid within the sensed volumeby individually pulsing the heater 30 of a pair and comparing multiplemagnitudes of temperature as sensed by the sensors of multiple pairs.For example, controller 230 may pulse the heater 30 of pair 1 andthereafter compare the temperature sensed by sensor 34 of pair 1, thetemperature sensed by sensor 34 of pair 0, the temperature sensed bysensor 34 of pair 2, and so on, each temperature resulting from thepulsing of the heater 30 of pair 1. In one implementation, thecontroller may utilize the analysis of the multiple magnitudes oftemperature from the different sensors vertically along the liquidinterface, resulting from a single pulse of heat, to determine whetherliquid or air is adjacent to the heater sensor pair having the heaterthat was pulsed. In such an implementation, controller 230 carries outsuch pulsing and sensing by separately pulsing the heater of each pairof the array and analyzing the resulting corresponding multipledifferent temperature magnitudes until the level of the liquid withinthe sensed volume is found or identified.

In another implementation, the controller may determine the level ofliquid within the sensed volume based upon the differences in themultiple magnitudes of temperature vertically along the liquid interfaceresulting from a single heat pulse. For example, if the magnitude oftemperature of a particular sensor drastically changes with respect tothe magnitude of temperature of an adjacent sensor, the drastic changemay indicate that the level of liquid is at or between the two sensors.In one implementation, the controller may compare differences betweenthe temperature magnitudes of adjacent sensors to a predefined thresholdto determine whether the level liquid is at or between the knownvertical locations of the two sensors.

In yet other implementations, a controller, such as controller 230described above, determines the level of liquid within the sensed volumebased upon the profile of a transient temperature curve based uponsignals from a single sensor or multiple transient temperature curvesbased upon signals from multiple sensors. In one implementation, acontroller, such as controller 230 described above, determines a levelof liquid within the sensed volume by individually pulsing the heater 30of a pair and comparing the transient temperature curve, produced by thesensor of the same pair, relative to the predefined threshold or apredefined curve to determine whether liquid or air is adjacent to theindividual heater/sensor pair. Controller 230 carries out such pulsingand sensing for each pair of the array until the level of the liquidwithin the sensed volume is found or identified. For example, controller230 may first pulse heater 30 of pair 0 and compare the resultingtransient temperature curve produced by sensor 34 of pair 0 to apredetermined threshold or predefined comparison curve. Thereafter,controller 30 may pulse heater 30 of pair 1 and compare the resultingtransient temperature curve produced by sensor 34 of pair 1 to apredetermined threshold or predefined comparison curve. This process isrepeated until the level of the liquid is found or identified.

In another implementation, a controller, such as controller 230described above, determines a level of liquid within the sensed volumeby individually pulsing the heater 30 of a pair and comparing multipletransient temperature curves produced by the sensors of multiple pairs.For example, controller 230 may pulse the heater 30 of pair 1 andthereafter compare the resulting transient temperature curve producedsensor 34 of pair 1, the resulting transient temperature curve producedby sensor 34 of pair 0, the resulting transient temperature curveproduced by sensor 34 of pair 2, and so on, each transient temperaturecurve resulting from the pulsing of the heater 30 of pair 1. In oneimplementation, the controller may utilize the analysis of the multipletransient temperature curves from the different sensors vertically alongthe liquid interface, resulting from a single pulse of heat, todetermine whether liquid or air is adjacent to the heater sensor pairhaving the heater that was pulsed. In such an implementation, controller230 carries out such pulsing and sensing by separately pulsing theheater of each pair of the array and analyzing the resultingcorresponding multiple different transient temperature curves until thelevel of the liquid within the sensed volume is found or identified.

In another implementation, the controller may determine the level ofliquid within the sensed volume based upon the differences in themultiple transient temperature curves produced by different sensorsvertically along the liquid interface resulting from a single heatpulse. For example, if the transient temperature curve of a particularsensor drastically changes with respect to the transient temperaturecurve of an adjacent sensor, the drastic change may indicate that thelevel of liquid is at or between the two sensors. In one implementation,the controller may compare differences between the transient temperaturecurves of adjacent sensors to a predefined threshold to determinewhether the level liquid is at or between the known vertical locationsof the two sensors.

FIGS. 11 and 12 illustrate sensor 700, an example implementation ofsensor 500. Sensor 700 comprises carrier 722, liquid interface 224,electrical interface 726, driver 728 and collar 730. Carrier 722 issimilar to carrier 222 described above. In the example illustrated,carrier 722 comprises a molded polymer. In other implementations,carrier 722 may comprise a glass or other materials.

Liquid interface 224 is described above. Liquid interface 224 is bonded,glued or otherwise adhered to a face of carrier 722 along the length ofthe carrier 722. Carrier 722 may be formed from, or comprise, glass,polymers, FR4 or other materials.

Electrical interconnect 226 comprises a printed circuit board havingelectrical contact pad 236 are making electrical connection withcontroller 230 (described above with respect to FIGS. 3-5). In theexample illustrated, electrical interconnect 226 is bonded or otherwiseadhered to carrier 722. Electrical interconnect 226 is electricallyconnected to driver 728 as well as the heaters 530 and sensors 534 ofliquid interface 224. Driver 728 comprises an application-specificintegrated circuit (ASIC) which drives heaters 530 and sensors 534 inresponse to signals received through electrical interconnect 726. Inother implementations, the driving of heaters 530 and the sensing bysensors 534 may alternatively be controlled by a fully integrated drivercircuit in lieu of an ASIC.

Collar 730 extends about carrier 722. Collar 730 serves as a supplyintegration interface between carrier 722 and the liquid container inwhich sensor 700 is used to detect level of liquid within a volume. Insome implementations, collar 730 provides a liquid seal, separatingliquid contained within the volume that is being sensed and theinterconnect 726. As shown by FIG. 11, in some implementations, driver728 as well as the electrical connections between driver 728, liquidinterface 224 and electrical interconnect 722 are further covered by aprotective electrically insulating wire bond adhesive or encapsulant 735such as a layer of epoxy mold compound.

FIGS. 13-15 illustrate sensor 800, another implementation of sensor 500.Sensor 800 is similar to sensor 700 except that sensor 800 comprisescarrier 822 in place of carrier 722 and omits the electricalinterconnect 726. Carrier 822 comprises a printed circuit board or otherstructure having embedded electrical traces and contact pads tofacilitate electrical connection between various electronic componentsmounted upon carrier 722. In one implementation, carrier 822 comprises acomposite material composed of woven fiberglass cloth with an epoxyresin binder. In one implementation, carrier 222 comprises aglass-reinforced epoxy laminate sheet, tube, rod or printed circuitboard, such as an FR4 printed circuit board.

As shown by FIGS. 14 and 15, liquid interface 224 is an easily bonded tocarrier 822 by a die attach adhesive 831. Liquid interface 224 isfurther wire bonded to the acumen are driver 728 and the electricalcontact pads relate 36 provided as part of carrier 822. Encapsulant 735overlays or covers the wire bonds between liquid interface 224, driver728 and the electrical contact pads 836. As shown by FIG. 13, collar 730is positioned about encapsulant 735 between a lower end of liquidinterface 224 and the elect contact pads 836.

FIGS. 16, 17 and 18A-18E illustrate one example method for formingsensor 800. FIG. 16 illustrates method 900 for forming sensor 800. Asindicated by block 902, liquid interface 224 is attached to carrier 822.As indicated by block 904, driver 728 is also attached to carrier 822.FIG. 18A illustrates carrier 822 prior to the attachment of liquidinterface 224 and driver 728. FIG. 18B illustrate sensor 800 after theattachment of interface 224 and driver 728 (shown in FIG. 14) withadhesive layer 831. In one implementation, the adhesive layer 831 isstamped upon carrier 822 to precisely locate the adhesive 831. In oneimplementation, the attachment of liquid interface to 24 and driver 728further includes curing of the adhesive.

As indicated by block 906 of FIG. 16, liquid interface 224 is wirebonded to contact pads 836 of carrier 822 serving as an electricalinterconnect. As indicated by block 908 in FIG. 16, the wire bonds 841shown in FIG. 18C are then encapsulated within encapsulant 735. In oneimplementation, the encapsulant is cured. As shown by FIG. 17, in oneimplementation, multiple sensors 800 may be formed as part of a singlepanel 841. For example, a single FR4 panel having electricallyconductive traces and contact pads for multiple sensors 800 may be usedas a substrate upon which liquid interfaces to 24, drivers 728, andencapsulant may be formed. As indicated by block 910 FIG. 16, in such animplementation, the individual sensors 800 are singulated from thepanel. As illustrated by FIG. 18E, in applications where the sensor 800is to be incorporated as part of a liquid or fluid supply, collar 730 isfurther secured to carrier 822 between the wire bonds 841 and the lowerend 847 of liquid interface 224. In one implementation, collar 730 isadhesively bonded to carrier 822 by an adhesive that is subsequentlycured.

Although the present disclosure has been described with reference toexample implementations, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the claimed subject matter. For example, although differentexample implementations may have been described as including one or morefeatures providing one or more benefits, it is contemplated that thedescribed features may be interchanged with one another or alternativelybe combined with one another in the described example implementations orin other alternative implementations. Because the technology of thepresent disclosure is relatively complex, not all changes in thetechnology are foreseeable. The present disclosure described withreference to the example implementations and set forth in the followingclaims is manifestly intended to be as broad as possible. For example,unless specifically otherwise noted, the claims reciting a singleparticular element also encompass a plurality of such particularelements. The terms “first”, “second”, “third” and so on in the claimsmerely distinguish different elements and, unless otherwise stated, arenot to be specifically associated with a particular order or particularnumbering of elements in the disclosure.

What is claimed is:
 1. A liquid container comprising: a chamber forminga volume containing a liquid; an elongated strip extending into thevolume containing the liquid, the strip supported along a side of thevolume such that a face of the strip adjacent the side of the volume isnot opposed by the liquid; a plurality of heaters supported by the stripalong the strip; and a plurality of temperature sensors supported by thestrip along the strip, wherein the plurality of heaters and theplurality of temperature sensors are supported by a first surface of thestrip, wherein the temperature sensors are to output signals indicativeof dissipation of heat from the heaters to indicate a level of theliquid within the volume.
 2. The liquid container of claim 1, whereinthe plurality of heaters and the plurality of temperature sensors form aplurality of stacks supported by the first surface of the strip, eachrespective stack in the plurality of stacks comprising a respectiveheater and a respective temperature sensor that are one over another inrespective different layers above the first surface of the strip.
 3. Theliquid container of claim 1, further comprising: a carrier supportingthe strip; an electrical interconnect electrically connected to thetemperature sensors; and a collar extending about the carrier andproviding a liquid seal to separate the liquid in the volume from theelectrical interconnect.
 4. The liquid container of claim 3, wherein theelectrical interconnect comprises contact pads.
 5. The liquid containerof claim 1, wherein the electrical interconnect is covered by anelectrically insulating encapsulant.
 6. The liquid container of claim 1,wherein the electrical interconnect is covered by an electricallyinsulating adhesive.
 7. The liquid container of claim 1, furthercomprising: a carrier, wherein the strip is glued to the carrier.
 8. Theliquid container of claim 1, further comprising: a carrier, wherein thestrip is adhered to the carrier, and the carrier is suspended from a topof the chamber.
 9. The liquid container of claim 1, further comprising:an electrical interconnect electrically connected to the temperaturesensors, the electrical interconnect comprising a printed circuit board,the printed circuit board to electrically connect to a controller. 10.The liquid container of claim 1, further comprising: a driver to drivethe heaters and the temperature sensors in response to signals receivedthrough an electrical interconnect.
 11. The liquid container of claim10, wherein the driver comprises an application-specific integratedcircuit (ASIC).
 12. The liquid container of claim 10, wherein thedriver, the electrical interconnect, the heaters, and the temperaturesensors are covered by an electrically insulating adhesive orencapsulant.
 13. The liquid container of claim 1, wherein the elongatedstrip comprises silicon.
 14. The liquid container of claim 1, whereineach of the heaters comprises a resistor.
 15. The liquid container ofclaim 1, wherein the plurality of heaters comprises a first heater, andwherein the plurality of temperature sensors comprises a temperaturesensor spaced from the first heater by less than or equal to 20 μm. 16.The liquid container of claim 1, further comprising: a carriersupporting the elongated strip, wherein the elongated strip comprises: afirst layer supporting the plurality of heaters; and a second layersupporting the plurality of temperature sensors.
 17. The liquidcontainer of claim 1, wherein activation of each respective heater ofthe plurality of heaters generates a heat pulse for sensing by arespective temperature sensor of the plurality of temperature sensors.18. A liquid container comprising: a chamber forming a volume containinga liquid; a plurality of heaters supported along the chamber, theheaters at different depths within the volume; a plurality oftemperature sensors supported along the chamber, the temperature sensorsat different depths within the volume, wherein the temperature sensorsare to output signals in response to heat pulses from the heaters, thesignals indicating a level of the liquid within the volume; anelectrical interconnect to communicate with a controller; and anencapsulant covering the plurality of heaters, the plurality oftemperature sensors, and the electrical interconnect.
 19. The liquidcontainer of claim 18, further comprising a driver to drive the heatersand the temperature sensors in response to signals received through anelectrical interconnect, wherein the encapsulant further covers thedriver.
 20. A liquid container comprising: a chamber forming a volumecontaining a liquid; an elongated strip extending into the volumecontaining the liquid; a plurality of heaters supported by the stripalong the strip; a plurality of temperature sensors supported by thestrip along the strip, wherein the temperature sensors are to outputsignals indicative of dissipation of heat from the heaters to indicate alevel of the liquid within the volume; a carrier supporting the strip;an electrical interconnect electrically connected to the temperaturesensors; and a collar extending about the carrier and providing a liquidseal to separate the liquid in the volume from the electricalinterconnect.